Sewage Lagoons: The Essential Guide to Efficient and Effective Wastewater Treatment

A type of tank where wastewater or sewage from a sewer system is directed to is referred as sewage lagoon. They are also known as facultative lagoons or effluent ponds, depending on their design and function respectively. Because they are a low-cost solution for the treatment of human, animal and industrial wastewaters, such pools play an important role in wastewater management.

Understanding Sewage Lagoons

Waste stabilization, containment and management of sewage requires lagoons. They are large shallow open-air lakes which serve as temporary holding tanks for sewage resulting in treated effluent at the end due to natural biological processes that decomposition waste material. This is made possible by presence of algae, sun and wind as well as microorganisms in the water thereby making these types of pools preferable options for treating waste water.

How Sewage Lagoons Work

Aerobic (with oxygen) and anaerobic (without oxygen) processes are involved in the operation of a lagoon. The depth and design of the lagoon determine which process is predominant. In shallower lagoons can support anaerobic processes in the lower depths.

1. Aerobic Processes:  The aerobic bacteria are grown by the mixture of oxygen from atmosphere and water. When they decompose organic matter, these bacteria convert it into carbon dioxide, water as well as other less harmful substances. Algae are key players in this process because they photosynthesize oxygen required by these bacteria.
2. Anaerobic Process: Anaerobic bacteria take over in deeper layers where there is minimal oxygen levels. These organisms break down organic material without any oxygen thus producing methane, carbon dioxide and other waste products. As time goes by, this process helps to break down solid waste that settles at the bottom.
3. Algae and Wind Action: Bacteria together with algae make the water have a greenish tint caused by decomposition of waste materials. Water evaporation is another way in which wind action works. This also enables mosquito breeding to be done away with via facilitating oxygen diffusion or wave formation which will not give them an opportunity for laying eggs.

Structural Requirements of a Sewage Lagoon

Design and construction of a sewage lagoon is important in determining its effectiveness and life span. The following are some key structural requirements that must be met for the lagoon to function properly:

1. Depth and Slope: For aerobic processes, the depth should not exceed one meter. The banks should be constructed using concrete, gravel or rocks, with a slope of approximately 20 degrees on either side. This design helps prevent erosion from wave action and maintains the structure’s integrity over time.
2. Vegetation Control: The surrounding areas and banks should be kept free from vegetation such as grasses, trees or bushes that could block sunlight, which is essential. Additionally, water should be free from objects such as still patches that would disrupt wave actions.
3. Fencing: The area should be surrounded by a high fence with a lockable gate to prevent children and animals from entering it, ensuring safety and preventing it from getting contaminated.

Lagoon Overflows

There is a probability of having an overflow lagoon opposite the inlet to the effluent carrying pipe in some sewage farms. In other set ups, there are a number of basins which are separated by walls or banks and last or bottom basin has overflow. The function of such overflows is to empty excess water remaining after evaporation from the system.

Nowadays, water removal is mainly done through evaporation with overflows being necessary only during intense rain periods. However, for older systems that are still applicable today, care must be taken to prevent overflows from causing floods and marshy places which may end up being breeding sites for mosquitoes or lead into pollution of drinking water as well as its surroundings.

Maintenance of Sewage Lagoons

The effective operation of a sewage lagoon depends on proper maintenance practices being carried out. There is need for continuous operation of such sewer plants; thus, failing such could pose danger to human health. Signs indicating poor functioning sewers include excessive overflow volumes as well as mosquito breeding incidence and pungent smell.

Regular inspections as well as maintenance are essential to establish and address any issues that may arise. The following are some critical maintenance tasks:

1. Review the Banks: For erosion, damage or improper slope, the banks of a lagoon need to be examined. To prevent further deterioration with time, timely repairs should be made on any identified issue.
2. Vegetation Control: Vegetation inside or around the lagoon should be removed so that sunlight and wind can prevail over it. In particular, managing grass on the water edge will help in preventing mosquito breeding.
3. Monitor Water Quality: Healthy algae growth in lagoon is indicated by light flecked green color of water within it. Any change in color, smell or stagnant areas on its surface must be looked into and addressed.
4. Fence and Gate Maintenance: For unauthorized entry, the fence and gate surrounding the lagoon must always be maintained in good working condition. Prompt repairs should thus be done whenever there is any damage to either of them.
5. Blue Flame Biodigesters: Blue Flame Biodigesters can be used as part of the lagoon’s maintenance routine. These biodigesters introduce a proprietary blend of aerobic and anaerobic bacteria into the lagoon, helping to break down organic matter and reduce odors. The main benefits include faster breakdown of solids, reduced need for lagoon dredging, improved water quality, and decreased odor levels. Regular application of the bacterial blend, typically monthly or quarterly, ensures continuous treatment of the sewage and effective maintenance of the lagoon.

Advantages and Disadvantages of Sewage Lagoons

Advantages

Cost-Effective: Sewage lagoons are relatively inexpensive to construct and maintain compared to other wastewater treatment options. They require minimal mechanical equipment and can be operated with limited technical expertise.

Eco-friendly: Sewage lagoons rely on natural processes to treat wastewater, making them an environmentally friendly option. The use of sunlight, wind, and microorganisms reduces the need for chemical additives and energy-intensive processes.

Low Energy Requirements: Facultative lagoons, in particular, require very little energy to operate, as they rely on natural aeration and biological processes.

Simple Operation: The operation of a sewage lagoon is relatively straightforward, requiring minimal intervention once the lagoon is constructed and maintained.

Disadvantages

Land-Intensive: Sewage lagoons require a significant amount of land, making them less suitable for densely populated or urban areas.

Odor Issues: Sewage lagoons can emit odors, particularly during certain times of the year when biological activity is high. Proper design and maintenance can help mitigate this issue, but it can still be a concern for nearby residents.

Climate Sensitivity: The effectiveness of a sewage lagoon can be influenced climate conditions, such as temperature, sunlight, and wind. In colder climates, the treatment process may slow down, requiring additional measures to maintain efficiency.

Potential for Mosquito Breeding: If not properly maintained, sewage lagoons can become breeding grounds for mosquitoes, posing a health risk to nearby communities.

Residential Sewage Lagoons

Residential sewage lagoons are commonly used in rural areas, where septic systems may not be suitable due to soil conditions or space limitations. In these systems, wastewater from residential areas enters a septic tank, where solids settle at the bottom, and the liquid effluent flows into the lagoon for further treatment.

The treatment process in residential sewage lagoons is influenced by factors such as sunlight, temperature, and wind. The lagoon relies on natural processes to break down the waste and treat the effluent, making it a simple and effective solution for wastewater management in rural communities.

Sewage Lagoon Design Considerations

The design of a sewage lagoon is critical to its success. Several factors must be considered during the design process to ensure the lagoon functions effectively and meets regulatory requirements:

1. Location: The location of the lagoon should have adequate space and suitable terrain for construction. The groundwater table should be low to prevent contamination, and the area should be free of vegetation that could obstruct sunlight and wind.
2. Liner Selection: A strong and flexible geomembrane liner is typically used to prevent seepage and protect the surrounding environment from contamination. The liner must be properly installed and secured along the edges of the lagoon.
3. Overflow Protection: The lagoon should be designed with overflow protection, such as spillways or drainage pipes, to prevent flooding during heavy rainfall. Overflow areas should be lined to direct runoff to a safe discharge location.
4. Aeration: While some lagoons rely on natural aeration, others may require ,mechanical aeration systems to increase treatment capacity and efficiency. The need for aeration should be considered during the design process.
5. Fencing and Signage: The lagoon should be surrounded by a secure fence with clear signage to prevent unauthorized access and ensure safety.

Purpose of Algae in Sewage Lagoons

Algae play a vital role in the functioning of sewage lagoons. They produce oxygen through photosynthesis, which is essential for the aerobic bacteria that break down the organic material in the sewage. Algae also help to maintain the balance of the ecosystem within the lagoon by providing a food source for microorganisms.

The presence of algae is a sign of a healthy lagoon, as they contribute to the overall efficiency of the wastewater treatment process. However, excessive algae growth can lead to issues such as clogging or reduced water quality, so it is important to maintain the proper balance within the lagoon.

Potential Contamination and Risks

While they are designed to treat wastewater, there is a risk of contamination if the system is not properly maintained or if the lagoon is not designed to handle the volume of waste being treated. Contaminants such as bacteria, viruses, and chemicals can seep into the groundwater or be carried by surface water, posing a risk to public health and the environment.

To mitigate these risks, it is important to conduct regular inspections and maintenance, ensure the lagoon is properly lined and sealed, and adhere to regulatory guidelines for lagoon design and operation.

FAQ

What can be done to manage odors during turnover?

Odors are common with sewage lagoon turnover especially during seasonal changes when water layers mix. To address these, in Kenya, facilities might begin aeration earlier in the season to hasten the process of lagoon turnaround. Sprays meant for deodorizing only mask smells temporarily and should never be sprayed into the lagoons directly. However, increasing dissolved oxygen (DO) through aeration or use of approved chemicals may help alleviating this but may necessitate permission from relevant environmental authorities within Kenya.

Can one utilize lagoon water or effluent for lawn irrigation, dust control on roads or crop irrigation purposes?

Using such water from either lagoons or effluent in irrigating lawns, controlling road dust or watering crops requires caution. It is not automatic that these applications fall within the standard wastewater management rules. In order to ensure its safety and compliance with environmental standards it will require specific authorization from NEMA (National Environment Management Authority) and other concerned parties.

Can I accept hauled wastes, septage, or other non-standard wastewaters?

In case you have a sewage lagoon, you need to review any such requests about accepting hauled wastes (including but not limited to septage and contaminated groundwater). You can accept them but only if they do not cause the treatment capacity of the lagoon to be exceeded and breach any permit conditions. In cases where your permit does not specify this, you might have to seek permission from or modify your permits with the relevant authority.

What sort of security fencing is considered adequate?

To prevent unauthorized access, it is necessary that sewage lagoons are enclosed by a secure fence. Gates should be wide enough for maintenance vehicles and should be kept locked at all times. Warning signs shall be displayed around its perimeter. If there is any populated area near the lagoon, additional fences or barriers may be needed to prevent entry by children or animals.

What authorizations/notifications/permits are required if you add aerators, mixers, or diffusers to the lagoons?

Adding aerators, mixers, or diffusers to sewage lagoons may require a permit from the relevant environmental authority, such as NEMA. For systems serving the public, a formal construction permit is typically needed. For private systems, it is advisable to notify the authorities to ensure compliance with environmental standards and improve the efficiency of the lagoon.

How do I check my sludge levels?

Sludge levels in a sewage lagoon can be checked using a boat to measure sludge depth at various points within the lagoon. This can be done using a sludge judge or similar tool. During cooler seasons, if ice forms (in high-altitude areas), a grid can be marked on the ice, and holes can be bored to measure sludge levels.

How do you check for lagoon leakage?

Lagoon leakage in Kenya can be detected through visual inspections for signs of flowing or ponding water around the lagoon. An Exfiltration Test, comparing lagoon water levels with evaporation and precipitation rates, can also be used. Groundwater monitoring wells provide a more accurate method for detecting leakage and ensuring environmental compliance.

How much algae is too much?

While the exact amount isn’t specified, excessive algae can disrupt the performance of a sewage lagoon and affect water quality. Regular monitoring is essential to manage algae growth effectively.

How do you control algae growth?

Algae growth in Kenyan sewage lagoons can be controlled through various methods, including the use of barley straw, enhancing aeration, and maintaining appropriate nutrient levels in the water. Consulting with local environmental authorities for specific guidelines and recommendations is advisable.

How long do sewage lagoons last?

Sewage lagoons typically last between 20 to 50 years, depending on factors like maintenance, design, and environmental conditions. Regular upkeep can extend their lifespan.

Conclusion

Sewage lagoons offer a cost-effective and environmentally friendly solution for wastewater treatment in rural and suburban areas. By relying on natural processes to break down waste, sewage lagoons provide an efficient and sustainable method for managing sewage and protecting public health. However, proper design, construction, and maintenance are critical to the success of a sewage lagoon.

Incorporating advanced technologies like Blue Flame Biodigesters into the maintenance routine further enhances the lagoon’s effectiveness. These biodigesters accelerate the breakdown of solids, reduce odors, and improve overall water quality, minimizing the need for intensive maintenance and ensuring that the lagoon operates at peak efficiency.

By understanding and implementing the key factors that influence the operation of sewage lagoons, including the use of Blue Flame Biodigesters, communities can ensure effective wastewater treatment for years to come.